Conventionally, an exhaust gas purifying catalyst for use in an automobile or the like is known to include an oxide of alkali earth and rare earth supported by a noble metal such as Pt, Rh, Pd, and others.
While the above exhaust gas purifying catalyst processes an exhaust gas, sintering sometimes occurs to the noble metal (especially Pt), which results in deterioration in catalytic activity. In such cases, an oxidation treatment process and a reduction treatment process are applied after processing of the exhaust gas. There is a proposal for a method for recovering the catalytic activity in that manner (see Patent Literature 1).    Patent Literature 1: Unexamined Japanese Patent Publication No. 8-144748